This application claims priority under 35 U.S.C. xc2xa7 119(a)-(d) from Russian Patent Application No. 98123248, filed Dec. 29, 1998 (now Russian Federation Patent No. 2142661), and also claims priority under 35 U.S.C. xc2xa7 119(a)-(d) from International Application No. PCT/RU99/00245, filed Jul. 21, 1999.
1. Field of the Invention
The invention relates to optoelectronic technology, and more particularly, to effective, powerful, superbright and compact semiconductor diodes that are sources of spontaneous emission having a narrow beam pattern.
2. Description of the Related Art
The injection incoherent emitter (hereafter referred to as the xe2x80x9cEmitterxe2x80x9d) is a device that converts electricity into optical emission of a specific spectral composition and spatial distribution (in the absence of an optical resonator). Different types of injection incoherent emitters are known for a broad range of wavelengths, from infrared to blue and ultraviolet emissions. These emitters include LEDs that produce surface emission, such as bright multipass LEDs (see, for example, F. A. Kish, et al., Appl. Phys. Lett., Vol. 64, No. 20, pp. 2839-2841 (1994); H. Sugawara, et al., Jap. J. Appl. Phys., Vol. 31, No. 8, pp. 2446-2451 (1992); M. Watanabe, et al., U.S. Pat. No. 5,537,433, Jul. 16, 1996; S. Nakamura, et al., Jap. J. Appl. Phys. Lett., Vol. 34, L1332 (1995)). These emitters also include end emitters (see, for example, A. T. Semenov, et al., Electron. Lett., Vol. 29, pp. 854-857 (1993); G. A. Alphonse, et al., IEEE J. of Quant. Electronics, Vol. QE-24, pp. 2454-2457 (1988)). Widespread use of these emission sources, however, is hampered by their insufficiently high efficiency, strength and power of the emission. The divergence of these emission sources is also too high for a number of applications.
An exemplary Emitter is described in F. A. Kish, et al., Appl. Phys. Lett., Vol. 64, No. 20, pp. 2839-2841 (1994). This exemplary Emitter is multipass and includes a heterostructure comprising semiconductor compounds AlGaInP. This Emitter contains an active layer with a broad forbidden band equal to Ea (eV), and thickness da in the range of 1-1.5 xcexcm. This Emitter also has two optically uniform cladding layers, one of p-type conductance and the other of n-type conductance. Each cladding layer comprises one sublayer arranged, respectively, on the first and second surfaces of the active layer; the second surface being opposite to the first surface. Emission output areas (hereafter referred to as the xe2x80x9cOAxe2x80x9d) are located on surfaces of the cladding layers not adjacent to the active layer. These OA are made of a homogeneous semiconductor compound transparent to the emitted light, and more particularly, are made of GaP having p- and n-types of conductance, respectively. The OA are in the form of rectangular parallelepipeds having inner surfaces of area Sin (xcexcm2) placed on the surfaces of the cladding layers not adjacent to the active layer. Side surfaces of the parallelepipeds form linear slope angles "psgr" of 90xc2x0 with the inner and outer surfaces of the OA, as well as with the active layer plane. An injection area for the current carriers having an area Sia (xcexcm2) coincides with the active layer. The injection area is created by forming ohmic contacts on the p- and n-type OA. Metal coating layers are also required. When a direct current is applied in the injection area, non-equilibrium carriers recombine, producing spontaneous emission that propagates from the injection area to all sides of the active layer, including to both OA of p- and n-types. After disorderly, multiple reflections, a certain portion of the spontaneous emission is removed at various angles from the LED through the output surfaces. These output surfaces are located partially on the outer surface of the p-type OA and on the side surfaces of the OA of both types. The divergence angle xcex81 of the output emission in the vertical planes and the divergence angle xcex82 of output emission in the horizontal planes have the maximum permissible value (up to 180xc2x0). The vertical planes are defined herein to be planes perpendicular to the active layer plane. The horizontal planes are defined herein to be planes perpendicular to the vertical planes and located on the output surfaces. Note that each direction of emission that passes through the horizontal plane could correspond to its own vertical plane that contains emission beams of the indicated direction. The known Emitter disclosed in F. A. Kish, et al., Appl. Phys. Lett., Vol. 64, No. 20, pp. 2839-2841 (1994) outputs light having a wavelength of 604 nanometers, with an external efficiency of 11.5% and with a light emission power (relative to 1A of current) of 93.2 lm/A. The density of the working current for continuous operating conditions does not exceed 100 A/cm2. The direction of the light rays in relation to the output surfaces in this case is disorderly, i.e., chaotic.
An object of the present invention is to provide an Emitter with increased external efficiency, increased energy and power, and increased emission intensity and light intensity. Another object of the present invention is to provide the possibility of directed, spontaneous emission for a broad range of directions. A further object of the present invention is the creation of multi-beam Emitters that emit from lines and arrays of emitters, with independent inclusion of each beam. It is an object of the present invention to provide an Emitter having the foregoing features using simplified manufacturing technology.
One aspect of the present invention is an injection incoherent emitter that comprises a heterostructure and at least one emission output area. The heterostructure comprises at least one active layer, a plurality of cladding layers, and a plurality of ohmic contacts. The at least one emission output area is located on at least one side of the active layer. The emission output area adjoins at least one of the cladding layers. The emission output area is transparent for emission. The emission output area comprises at least one emission output area layer having a refractive index noaq, where q=1, 2, . . . p is defined as a whole number that designates the ordinal number of the emission output area layer enumerated from a boundary of the emission output area with the heterostructure. The emission output area and the heterostructure together have an effective refractive index nef. The effective refractive index nef of the heterostructure and the emission output area and the refractive index noa1 of the emission output area are selected to satisfy the correlations:
arc cos(nef/noa1)xe2x89xa6arc cos(nef min/noal) 
and
nef min is greater than nmin. 
In the correlations, nef min is the minimum value of nef for heterostructures and adjoining emission output areas that produce spontaneous emission, and nmin is the least of the refractive indices in the heterostructure cladding layer.